Printing mechanisms, such as inkjet printers or plotters, often include an inkjet printhead which is capable of forming an image on many different types of media. The inkjet printhead ejects droplets of colored ink through a plurality of orifices and onto a given media as the media is advanced through a printzone. The printzone is defined by a plane created by the printhead orifices and any scanning or reciprocating movement the printhead may have back-and-forth and perpendicular to the movement of the media. Conventional methods for expelling ink from the printhead orifices, or nozzles, include piezo-electric and thermal techniques which are well-known to those skilled in the art. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, the Hewlett-Packard Company.
In a thermal inkjet system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains columnar arrays of heater elements, such as resistors, which are individually addressable and energized to heat ink within the vaporization chambers. The energy which is applied to a given resistor to heat the ink to the point of drop ejection is referred to as the turn-on energy. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
A printing mechanism may have one or more inkjet printheads, corresponding to one or more colors, or xe2x80x9cprocess colorsxe2x80x9d as they are referred to in the art. For example, a typical inkjet printing system may have a single printhead with only black ink; or the system may have four printheads, one each with black, cyan, magenta, and yellow inks; or the system may have three printheads, one each with cyan, magenta, and yellow inks. Of course, there are many more combinations and quantities of possible printheads in inkjet printing systems, including seven and eight ink/printhead systems.
Each process color ink is ejected onto the print media in such a way that size, relative position of the ink drops, and color of a small, discreet of process inks are integrated by the naturally occurring visual response of the human eye to produce the effect of a large colorspace with millions of discernable colors and the effect of a nearly continuous tone. In fact, when these imaging techniques are performed properly by those skilled in the art, near-photographic quality images can be obtained on a variety of print media using only three to eight colors of ink.
This high level of image quality depends on many factors, several of which include: consistent and small ink drop size, consistent ink drop trajectory printhead nozzle to the print media, and extremely reliable inkjet printhead nozzles which do not clog. Ink drop detectors may be employed in a printing mechanism to monitor nozzles for clogging, but it would be useful to also monitor drop size and trajectory. More specifically, it would be beneficial to be able to measure the numerous factors which affect ink drop size and trajectory.
Therefore, it is desirable to have a method and mechanism for effectively, efficiently, and economically measuring ink system characteristics which affect ink drop size and trajectory, such as viscosity, electrical conductivity, dye load, surface tension, drop firing turn-on energy, drop velocity, and ink age.